The objectives of this proposal are: 1) Operant conditioning of amplitudes of evoked potentials in trigeminal nucleus, midbrain reticular nucleus intercolliclaris, thalamic ventro-basal complex and centremedian-parafasicularis complex, and cortical oro-facial areas in rats. (The potentials are evoked by pulses to the primary trigeminal tract.) 2) Study and comparison of analgesic effects of the "neural biofeedback" in the loci just listed on oro-facial aversive reactions presumed related to trigeminal pain. Rats will be rewarded when evoked potential amplitude is changed. Five kinds of oro-facial nociceptive reactions will be compared before and during asymptotic levels of conditioning. This proposal may provide a clear demonstration of the functional significance of operant control of neural activity. This would be the first demonstration of such effects with evoked potentials, the conditioning of which has been demonstrated to be a non-trivially mediated, novel operant. The proposal aims at developing a new method of pain control with potential human clinical applications. The proposal to compare different conditioning effects in different brain loci may suggest differences in functional relevances of these loci for pain and analgesia. That is, control of some loci may produce analgesic effects, control of others may not. The former but not the latter loci would then appear to be connected to analgesia systems under conscious control.